Paternity testing can change the life of a child as well as the lives of the adults tested. Paternity testing provides highly accurate results within a few days. A rushed sample can be completed in as little as one to three days, Identigene reports, meaning that, in many cases, an answer regarding paternity can be provided before the baby leaves the hospital.
DNA samples obtained from the child's mother and alleged father often come from a simple swab of the inside of the cheek, which removes cells for testing. A newborn's cord blood can be used for his sample, or a cheek swab can also be used. Samples can easily be obtained before the baby leaves the hospital. Samples are taken at a testing facility or done by the alleged father and the mother and sent in to the laboratory for testing in special sample kits obtained at the pharmacy. If testing is done at a laboratory, identification to ensure a person is who he says he is must be presented.
A paternity test resembles a puzzle where pieces from the parents and child must match. DNA tests compare 15 DNA markers of both parents to those of the child. While testing can be done without the mother's DNA, her sample makes testing simpler and slightly more reliable. Since a child inherits genes from each parent, each locus, or marker location, must show one allele inherited from the mother and one from the father. If three or more DNA markers don't match between the alleged father and child, that person can't be the father of the child, IdentiGene explains, even if several other items do match. Almost any two people will have some matches.
A positive result depends not just on the number of allele matches but also on the probability of two people having the particular match. Some DNA matches are rarer than others and are assigned a higher value, called a paternity index, or PI value. Adding all the PI values together gives a combined paternity index, or CPI. A CPI of 100 indicates a 99 percent probability of paternity on an accredited paternity test report, which courts require for child support cases. Immigration cases require a CPI of 200, or 99.5 percent, according to IdentiGene. Reports don't claim a person is the biological father; instead, they state the person is not excluded as the father.
If a decision on paternity must be obtained before a child is discharged from the hospital, prenatal testing can be done, so that the results are known before the baby is born. Amniotic fluid cells or cells from near the placenta are removed and sent to the lab. This procedure is expensive and carries some risk to the fetus, says the American Pregnancy Association.
DNA testing can't distinguish between identical twin brothers as to which one is the father of the child, since identical twins carry the exact same DNA makeup. If the alleged father has died, samples from his parents can be used for testing, but only if his parentage is absolutely known. If his legal father was not his biological father, testing won't be accurate, Genelex warns.